I. Dental Conditions
A. Prevention of Plaque Formation, Caries, and Periodontal Disease
The relationship between bacterial plaque and the development of periodontal disease and caries has been thoroughly established (Axelsson, P., et al., J. Clin. Perio. 5: 133-151 (1978)). Periodontal disease is a major problem in humans, especially in adults 40 years of age or older, in the mentally retarded, and in the handicapped. For the latter two groups in particular this is due to an inability to properly care for the teeth. Periodontal disease is also widespread among animals, especially housepets. It has also been clearly shown that the bacterial flora of the gingival crevice is important in the etiology of periodontal disease (Slots, J., J. Clin. Perio. 6: 351-382 (1979)). Therefore, treatment of periodontal and caries diseases is directed to controlling this flora.
The most widely used approach to date has been mechanical cleaning methods such as tooth brushing. Although this method has proved to be fairly successful in treating individuals, there is still a high recurrence rate. There is also the problem of motivating people to good oral hygiene habits that they will maintain throughout their lives.
Although systemic administration of antibiotics has been shown to be a useful method of controlling the subgingival flora, discontinuation of therapy will result in the return of the potential pathogens to the pockets (6Genco, R. J., J. Perio. 52: 545-558 (1981)). Long-term antibiotic therapy has been used, but the potential dangers associated with this form of treatment, which include the development of resistant strains and superimposed infections, do not warrant its serious consideration.
Antibacterial agents such as chlorhexidine and quaternary ammonium salts in the form of mouth rinses, dentifrices, solutions and gels have not proven to be successful in preventing periodontal disease (see, for example, Ciancio, S. G., et al., Pharm. Therap. Dent. 3: 1-6 (1978)), as these agents are unable to affect the subgingival flora when administered in these forms (Goodson, J. M., et al., J. Clin. Perio. 6: 83-92 (1979)). In additi03 on, reported side effects of chlorhexidine, including staining and altered taste sensation, have resulted in limited usage. Attempts to reduce the staining and bitter taste by using dilute solutions and flavoring agents, respectively, have been only partially successful.
Sustained release has been reported to be achieved by embedding chlorhexidine in an ethyl cellulose polymer to form a film (Friedman, M., et al., J. Perio. Res. 17: 323-328 (1982); Friedman, M., et al., IADR Prog. and Abstr. 59: No. 905 (1980)). This dosage form was used in the local treatment of periodontal disease (Soskolne, W. A., et al., J. Perio. Res. 18: 330-336 (1983)) and in the treatment of plaque prevention in patients wearing orthodontic appliances (Friedman, M., et al., J. Dent. Res. 64: 1319-1321 (1985)). A drawback to this plaque preventative system was that although plaque accumulation was decreased by the application of a film composed of chlorhexidine embedded in an ethyl cellulose polymer, the effectiveness of the system in decreasing plaque accumulation was present only for a period of four days subsequent to administration of the film. Friedman, M., et al., (J. Dent. Res. 64: 1319-1321 (1985)), concluded that "clearly the conditions in the oral cavity and the formulation used do not, at present, facilitate such prolonged prevention of plaque accumulation." These authors also suggested that by altering the film components and method of preparation it might be possible in clinical use to sustain the necessary level of antibacterial agent release for longer periods. No suggestion was made in this publication as to how this could be accomplished.
Other antibacterial preparations for plaque prevention have been disclosed. Gaffar (U.S. Pat. No. 4,339,430) discloses an antibacterial oral composition containing an agent such as bis-biguanidohexanes or quaternary ammonium salts, and an additive which reduces staining of dental surfaces such as copolymers of glutamic acid, tyrosine, and alanine. This preparation was reported to be applied as a mouthwash or as a toothpaste.
Wahmi (U.S. Pat. No. 4,374,824) discloses dentifrices for cleaning and preserving teeth. Disclosed were compositions comprising ginger, magnesium silicate, sodium chloride, catechu, alum, seed and shell of sweet almond, pyrethrum, gum mastic, and tobacco. It was reported that gum mastic was added to the composition to assist in the prevention of tooth decay. The disclosed compositions were intended to be in the form of toothpaste or tooth powders. This patent does not disclose the possible long-term anti-plaque effect of the compositions; further, application of the disclosed compositions two to three times per day is required for anti-plaque activity.
Mastic has been used previously for other dental purposes. U.S. Pat. No. 4,668,188 (Wolfenson, G. B.) discloses the use of a curable mastic in the production of an oral impression tray for making impressions of teeth and jaw structures. Mastics have been used in the production of dental molds (U.S. Pat. No. 4,500,288, Von Weissenfluh, H.) and as an adhesive to secure dental articulators (U.S. Pat. Nos. 4,548,581 and 4,382,787, Hoffman, R. E.). U.S. Pat. Nos. 4,532,126 and 4,428,927 (Ebert, W. R., et al.) disclose chewable, filled, one-piece soft elastic gelatin capsules, made chewable by a masticatory substance, such as a synthetic mastic. U.S. Pat. No. 4,459,277 (Kosti, C. M.) relates to novel anti-plaque compositions for use in evaluating oral hygiene practices. In brief, the patent discloses a water-insoluble, water-immiscible dye emulsified in fine droplets or rupturable capsules. The patent discloses the use of mastic resin as well as alginates, and other gums as an insoluble media for dye dispersion. In particular, sodium carboxymethylcellulose is disclosed. Also disclosed is the possibility of incorporating antibacterial agents such as stannous fluoride into the compositions. Significantly, the Kosti patent is concerned with diagnostic rather than therapeutic applications. The patent fails to suggest compositions exhibiting long-term plaque preventive activity.
U.S. Pat. No. 3,956,480 (Dichter et al.) discloses the use of an anionic polymer to sorb a cationic germicidal polymer to a tooth surface.
A topical, sustained-release form of an antibacterial agent could help prevent the above-discussed side effects. Such a dosage form would be able to release the drug at a lower therapeutic level over a long period of time and thus might prevent the bitter taste and tooth staining.
B. Treatment of Tooth Hypersensitivity
Dental hypersensitivity, especially that arising from dentin and cementum hypersensitivity, is a frequently encountered problem in dentistry and a very troublesome clinical complaint. Hypersensitivity may occur wherever the dentin or cementum of a tooth is exposed by attrition or abrasion, or when the tooth's fine root surface is exposed by periodontal disease. In about 12% of erupted teeth, there is a developmental lack of protective covering of cementum at the cementoenamel junction. As a result, when the exposed dentin is subjected to mechanical, thermal, chemical or osmotic stimuli, the sensory nerves of the teeth become excited and a very painful response results. For example, people with hypersensitive teeth find it very painful to orally ingest certain forms of nourishment, such as liquids or foods that are hot or cold, sweet, hypertonic or contain citric acid. Everyday stimuli such as brushing the teeth may also be painful.
Many attempts have been made to control hypersensitivity of the teeth. For example, U.S. Pat. No. 3,863,006 (Hodosh, M.) describes the use of potassium, lithium or sodium nitrate; U.S. Pat. No. 4,751,072 and U.S. Pat. No. 4,631,185 (both to Kim, S.) describe the use of potassium bicarbonate and potassium chloride; U.S. Pat. No. 4,710,372 and U.S. Pat. No. 4,634,589 (both to Scheller, H. U.) describe the use of hydroxyapatite or fluorapatite; U.S. Pat. No. 4,057,621 Pashley, D. H., et al. ) describes the use of an alkali metal or ammonium oxalate; U.S. Pat. No. 4,415,549 (Shah, N. B.) describes the use of strontium EDTA, fluoride and ammonium glycyrrhizzinate; and, GB patent No. 990957 (Rosenthal, M. W.) describes the use of strontium for the control of hypersensitivity. The use of strontium ions to treat hypersensitivity was also disclosed in U.S. Pat. Nos. 3,122,483, 3,988,434 and 4,224,310.
However, although clinically the most effective for reducing tooth hypersensitivity, the use of strontium salts for the treatment of hypersensitivity is disliked by patients due to the tendency of strontium salts to leave an unacceptably salty taste or metallic taste in the mouth, even when used in a toothpaste form. Another major disadvantage of strontium dentifrice is the long period of time of application which is required to achieve the clinical effect.
A topical, sustained-release form of an agent capable of controlling dental hypersensitivity could help prevent undesirable taste side effects and still treat the hypersensitive condition. Such a dosage form would be able to release the agent controlling the hypersensitivity at a lower therapeutic level over a long period of time, for example, for weeks. Sustained localized release of the hypersensitivity agent, targeted directly to the hypersensitive site, would also solve the problem of the prolonged time and application currently required to obtain clinical effectiveness with strontium.
C. Root Canal Sterilization
A major concern in root canal dental procedures is the possibility of infection due to the introduction or cross-infection of bacteria, etc. into the affected region. Various surgical and endodontic methods have been developed in order to minimize the risk of infection (Miserendino, L. J., Oral Surg. Oral Med. Oral Pathol. 66: 615-619 (1988); Mondragon, E. J., Pract. Odontol. 8: 16-22 (1987); Hermsen, K. P. et al., Gen. Dent. 35: 355-356 (1987); Levy, G. et al., Zahnarzt 30: 441-442, 447-450 (1986); Chivian, N., Dent. Clin. North Amer. 28: 637-649 (1984); Linke, H. A. et al., Oral Surg. Oral Med. Oral Pathol. 55: 73-77 (1983); Agarwal, S. K. et al., J. Indian Dent. Assoc. 54: 323-326 (1982), which references are incorporated herein by reference). Camphorated parachlorophenol (CPK) is an antibacterial agent used to treat bacterial contamination in the root canal. The usual treatment involves dipping an absorbent point or gauze into a CPK solution and placing it in the root canal. The absorbent point remains in the root canal until the next visit to the dentist. The primary disadvantage of the current treatment is the limited exposure time of the active material which may lead to re-infection of the root canal.